Warer reducible epoxy coating composition

ABSTRACT

A homogeneous, water-reducible coating composition comprises a modified polyamine resin homogeneously reduced in an aqueous system comprising water and a low-molecular weight nitroparaffin. An epoxy resin can be added to the coating composition to form a stable emulsion.

This is a continuation, of application Ser. No. 143,916, filed Apr. 25,1980 now U.S. Pat. No. 4,352,898.

BACKGROUND

The present invention is directed to water-reducible coatingcompositions containing a modified polyamine resin and/or epoxy resin.

Organic solvents used in coating compositions have been identified as acontributor to air pollution. Since 1966 legislation and regulations onvolatile organic compounds have been directed to limiting the use oforganic compounds in coatings. Regulations have been issued to limit thevolatile organic content (VOC) of organic coatings to a maximum of 350grams per liter, where ##EQU1## where VOM=pounds of volatile organicmaterial per gallon of coating material as applied, and W=the volume ofwater per gallon in the coating as applied.

The volatile organic material is defined as any volatile compound ofcarbon, excluding methane, carbon monoxide, carbon dioxide, carbonicacid, metallic carbides or carbonates, ammonium carbonate, methylenechloride, 1,1,1-trichloroethane, and trichlorotrifluoroethane.

In order to achieve low VOC content, much attention is being directedtoward waterborne coatings. Advantages of waterborne coatings includereduced air pollution, limited fire and health hazards, and reducedusage of costly organic solvents.

Although a number of waterborne coatings are presently available, nonehas the high performance properties required to match existingcatalized, ambient temperature curing, solvent-borne coatings such astwo package epoxy coatings. Such high performance properties are vitalfor protection of metal surfaces on ships, aircraft, trucks, bridges,tanks and the like. Although each high performance coating has numerousunique requirements dictated by its end use, all high performancecoatings must be insensitive to water, solvents, and other fluids.

Water sensitivity is largely due to hydrophilic groups present in thepolymer binder and/or hydrophilic paint additives. Most water-bornecoatings have a preponderance of hydrophilic groups and hence are watersensitive. Solvent and fluid resistance properties are only obtainedwhen the coating binder is highly crosslinked, as is the case withcatalized systems. Unfortunately, most water-borne, ambient temperature,crosslinked systems such as latexes and water-soluble alkyds andacrylics, have insufficient crosslink densities for high performanceapplications.

Two component amino-epoxy coating systems have been considered for usein high performance, ambient temperature curing, water-borne coatingsystems. Because the most suitable epoxy resins and amino functionalcuring agents are not directly water reducible, various systems havebeen devised to overcome this technical difficulty.

One system that has been devised uses an emulsified epoxy resin. Theepoxy resin is either emulsified by a surfactant type emulsifying agentprior to use or emulsified during catalization by amino-functionalcuring agents which have been modified to have emulsifying properties.These emulsifier type curing agents are of two types: amino-functionalcuring agents which are neutralized by acids to form salts, such asdisclosed in U.S. Pat. No. 2,899,397 and 4,013,601; and aminofunctionalcuring agents (generally, special polyamide types) which are chemicallymodified with hydrophilic ether groups so they can be water reduced andemulsified, such as disclosed in U.S. Pat. No. 3,998,771 and 4,179,418.

These emulsified epxoy resin systems suffer from poor water resistance.Curing agents of the salt type remain water sensitive after curing dueto residual salt. Curing agents modified with the hydrophilic ethergroups remain permanently water sensitive. Furthermore, only lowmolecular weight curing agents can be used because of the very highviscosities which develop when the high molecular weight curing agentsare neutralized.

Curing agents useful in curing epoxy resins premulsified usingsurfactant type emulsifiers are disclosed in U.S. Pat. No. 4,086,179;4,104,223; 4,152,285; 3,816,366; and 3,956,208. All of these curingagents are low molecular weight polyamide types specially modified tomake them more water compatible by using low molecular weight carboxylicacids and/or hydrophilic polyamines in their makeup. Most have aminevalues greater than 300. Almost all polyamide type resins with aminevalues of greater than about 400 are inherently water reducible withoutmodification. The amine value is the number of milligrams of KOHequivalent per free amine groups in an one (1) gram sample of resin. Ingeneral, the higher the amine value of the resin the shorter the potlife of the catalized mixture and the more brittle the resulting coatingfilm. Because of the high amine value of these modified polyamide typecuring agents they have limited utility due to their short pot life.

A different approach to water-borne epoxy coatings is disclosed in U.S.Pat. Nos. 3,719,629 and 3,945,963. These patents disclose systems whichare water-reducible acrylic copolymers with pendant amino groups. Whencatalized, these pendant amino groups react with the epoxy resin to forma crosslinked acrylic coating film. Unfortunately, the resultingcoatings are not flexible. Also, the films are water and solventsensitive.

From the foregoing, it is evident that there is a need for a water-bornecoating composition that has a long pot life and that produces highperformance coatings which have solvent and water resistance, and aredurable and flexible.

SUMMARY

The present invention is directed to coating compositions with the abovefeatures. The invention is based on the discovery that modifiedpolyamine resins can be homogeneously reduced by water to form aqueoussystems comprising large amounts of water i.e., in excess of 50% byweight of the modified polyamine resin, by including a nitroparaffin inthe system. This can be accomplished without the use of emulsifiers andother dispersing aids. The nitroparaffin used is C_(n) X_(2n+2) where nis an integer from 1 to 4 and each X is independently selected from thegroup consisting of chlorine, hydrogen, or NO₂, where at least one butno more than 2 X's are NO₂. For example, the nitroparaffin can benitromethane, nitroethane, 1-nitropropane, 2-nitropropane,1-nitrobutane, 2-nitrobutane, and combinations thereof. The aqueoussystem includes nitroparaffin in amount of at least about 2%, andpreferably to about 50% by weight of the modified polyamine resin, andmore preferably from about 15 to about 25% by weight of the modifiedpolyamine resin.

The coating composition can be provided with or without an organicsolvent for the modified polaymine resin. It can be provided in kit formwhere a first container contains the modified polyamine resin and asecond container contains epoxy resin curable by the modified polyamineresin. The nitroparaffin can be included in either the first or secondcontainer. An organic solvent for the modified polyamine resin can beincluded in the first container and an organic solvent for the epoxyresin can be included in the second container. The amount of organicsolvent used is limited so that the coating composition as applied has avolatile organic content of no more than 450 grams per liter, andpreferably no more than 350 grams per liter. The composition formed bymixing contents of the first and second containers is water reducible,i.e., water can be added to reduce the viscosity of the composition.Water can be included in the container containing the nitroparaffin.

A remarkable feature of using a nitroparaffin to permit a modifiedpolyamine resin to be reduced by water is that unexpectedly, thenitroparaffin permits the epxoy resin to be emulsified. The combinationof the modified polyamine resin, nitroparaffin, epoxy resin, and wateris stable, has a long pot life, and can be used to form a durable waterand solvent-resistant, high gloss, flexible coating suitable for highperformance applications.

Other features and advantages of the present invention will becomebetter understood with reference to the appended claims and followingdescription.

DESCRIPTION

The present invention is directed to water-reducible epoxy coatingcompositions curable by modified polyamine resin curing agents. Theinvention is based on the discovery that modified polyamine resins whichby themselves are not water reducible or miscible, become homogeneouslywater reducible when a nitroparaffin is included in the system.Furthermore, it has been discovered that if epoxy resin is added to theabove system, it can be homogeneously dispersed or emulsified. Sincemodified polyamine resins are curing agents for epoxy resins, usefulproducts such as coatings and adhesives can be made from these systems.

By the term "dispersion" there is meant a two-phase system in which onephase, called the dispersed phase, is distributed as small particlesthrough the second phase called the continuous phase. By the term"emulsion" there is meant a two-phase liquid system in which smalldroplets of one liquid (the internal phase) are immiscible in, and aredispersed uniformly throughout, a second continuous liquid phase (theexternal phase).

Modified polyamine curing agents suitable for use in the coatingcompositions include those which inherently are soluble in water andthose which inherently are insoluble in water. By the term "inherentlyinsoluble" there is meant a curing agent that is not miscible with waterand cannot be homogeneously dispersed, emulsified or otherwise reducedby water without chemical modification and/or adding emulsifiers,dispersing aids and/or acids. It has been determined that merely byadding a nitroparaffin to an aqueous system, a modified polyamine resincuring agent which normally would form a separate phase with water canbe homogeneously reduced by water. By the term "reduced by water" thereis meant caused to be homogeneously miscible, emulsified, or dispersed.

Modified polyamines useful as curing agents in the coating compositionsof the present invention include those prepared by reacting aliphaticand cycloaliphatic polyamines with compounds known to react with theamine group. Curing agents derived from the reaction of polyamines withcompounds containing the glycidyl ether group (also known as the epoxygroup) or the carboxylic acid group have been found to be particularlyuseful. The reaction products of polyamines with the glycidyl ethergroup are known as polyamine-epoxy adducts in the trade and can beprepared using either mono, di, and/or poly glycidyl ether compounds.

Examples of polyamine--monoepoxide adducts are those based onmonofunctional aliphatic glycidyl ethers, styrene oxide,pentachlorophenyl glycidyl ether, reaction products of epichlorohydrinand bisphenol A containing phenolic hydroxyls and less than one epoxygroup per molecule, and epoxidized olefins from unsaturated fatty acidglycerides with less than one epoxy group per molecule.

Examples of polyamine-diepoxide adducts are those based on thediglycidyl ether of bisphenol A (DGEBA), the diglycidyl ether of4,4'-isopropylidenedicyclohexanol, diglycidyl ether of hydantoin,diepoxides obtained by epoxidation of aliphatic and/or cyclo-aliphaticpolyolefins, and diglycidyl ethers of polyoxyalkylene glycol.

Curing agents which are the reaction products of carboxylic acids andpolyamines are known as polyamide resin curing agents or polyamides inthe trade. They are usually prepared by condensation of the acidcomponent with excess amounts of polyalkylene polyamines, particularlypolythylene-polyamines. These amide type curing agents are classifiedaccording to the carboxylic acids and reaction conditions used in theirsynthesis. More precisely this amide class of curing agents arepoly-amino-amides and poly-amino-imidazolines. Poly-amino-imidazolinesare derivatives of poly-amino-amides prepared by heating to about 300°C. which causes cyclization, forming the imidazoline ring system.

The polyamide curing agents based on carboxylic acid can be classifiedas follows based on the carboxylic acid component:

1. monocarboxylic acids (also known as amido-amines)

2. polycarboxylic acids

a. C₃₆ dimer acids

b. dicarboxylic acids (other than C₃₆ dimer acids)

c. tri and poly carboxylic acids

1. trimerized C₁₈ fatty acids

2. tri and polycarboxylic acids (other than those based on C₁₈ fattyacids)

Polyamides based on dicarboxylic acids containing greater than 10 carbonatoms, and particularly those based on C₃₆ dicarboxylic acid, arepreferred to those based on other dicarboxylic acids such as C₈, C₉, andC₁₀ dicarboxlic acids because C₈, C₉, and C₁₀ dicarboxylic acids aremore hydrophilic and are less flexible than dicarboxylic acids havingmore than 10 carbon atoms. Thus a coating using a polyamide resin curingagent based on C₃₆ dicarboxylic acid can have good water resistance andflexibility. Preferably a coating comprising a polyamide resin is basedon polyamides resulting from the reaction of polyamines and mono- andpolycarboxylic acids, where less than about 75% by weight of thecarboxylic acids reacted with the polyamine are dicarboxylic acidshaving 10 or less carbon atoms.

Particularly valuable poly-amino-amides and poly-amino-imidazolines arebased on saturated and/or unsaturated monovalent natural fatty acids; onpolymeric, particularly dimeric and copolymeric fatty acids; ondicarboxylic acids obtained by carboxylation of unsaturated monovalentnatural fatty acids; and polycarboxylic acids obtained by the additionof di or tricarboxylic acids, or their derivatives, particularly maleicacid anhydrides, to natural unsaturated fatty acids.

Examples of other acids which can be used to form polyamides useful ascuring agents in the present invention include the following: palmiticacid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenicacid, dehydrated castor oil fatty acid, elastearic acid, or theirmixtures. The polymeric fatty acids used can be prepared from naturalfatty acids having one or more unsaturations by thermal or catalyticpolymerization or by copolymerization in the presence of polymerizablecompounds, such as styrene or its homologues, cyclopentadiene, and thelike. Carboxylation of the unsaturated fatty acids is likewise known andresults in the case of oleic acid in a dicarboxylic acid having 19carbon atoms. Other polycarboxylic acids are those which can be preparedby the addition of di- or tricarboxylic acids or their derivatives,particularly maleic acid anhydride to unsaturated fatty acid,particularly oleic acid.

In addition to the aforementioned poly-amino-amide andpoly-amino-imidazoline curing agents, polyepoxide adducts ofpoly-amino-amides and poly-amino-imidazolines (referred to herein aspolyamide epoxy adducts) prepared by the teachings of U.S. Pat. No.3,474,056, which is incorporated herein by this reference, are useful ascuring agents in this invention.

Particularly useful curing agents include Versamid and Genamid polyamideresins and the like reacted with epoxy resin according to the teachingsof U.S. Pat. No. 3,474,056. Versamid and Genamid polyamide resins areavailable from General Mills Corporation.

Preferably the polyamide resin has an amine value of less than about400. At amine values higher than about 400, a coating compositioncomprising the polyamide resin can have too short a pot life and thecoating films formed are not flexible. Most preferably the amine valueof the polyamide resin is from about 150 to about 300. The term "aminevalue" is defined as the miligrams of KOH which are equivalent to 1 gramof resin.

Preferably the modified polyamine resin is selected from the groupconsisting of (a) polyamine-epoxy adducts; (b) polyamides resulting fromthe reaction of polyamines and carboxylic acids selected from the groupconsisting of monocarboxylic acids, poly-carboxylic acids, andcombinations thereof, where less than about 75% by weight of thecarboxylic acids reacted with the polyamines are dicarboxylic acidshaving 10 or less carbon atoms; (c) polyamide-epoxy adducts; and (d)combinations thereof.

The nitroparaffin used in the present invention preferably has asufficiently low molecular weight to evaporate from the coating at aboutroom temperature. If the nitroparaffin did not evaporate from thecoating, it would remain in the coating, thereby reducing performanceproperties of the coating. Preferably the molecular weight of thenitroparaffin is less than about 150. The nitroparaffin has the formulaC_(n) X_(2n+2) where n is an integer from 1 to 4 and each X isindependently selected from the group consisting of chlorine, hydrogen,and NO₂, where at least one but no more than two X's are NO₂. Preferablythe nitroparaffin is selected from the group consisting of nitromethane,nitroethane, 1-nitropropane, 2-nitropropane, 1-nitrobutane,2-nitrobutane, and combinations thereof. Other suitable nitroparaffinsare 1,3 di-nitropropane and 1-chloro-nitropropane.

Preferred nitroparaffins are 2-nitropropane and nitroethane. This isbecause when a coating composition comprising a modified polyamineresin, nitroparaffin, water, and epoxy resin is formed with these twonitroparaffins, pot lives of 4 hours and greater have been achieved.When using 1-nitropropane and/or nitromethane, shorter pot lives in therange of 1 to 11/2 hours are achieved.

The coating composition contains sufficient nitroparaffin that themodified polyamine resin can be homogeneously reduced by water to forman aqueous system comprising water in an amount of at least 50% byweight of the modified polyamine resin curing agent. Generallynitroparaffin in an amount of at least 2% by weight of the curing agentis required. As the amount of the nitroparaffin in the composition isincreased, the pot life of the composition increases and the particlesize of the epoxy resin dispersed in the coating system decreases. Smallparticle size for the epoxy resins is desirable for stability and toform a uniform, coherent, durable coating. However, at nitroparaffincontents in excess of about 50% by weight of the polyamide resin, littleif any increase in pot life and decrease in the epoxy resin particlesize occur. Therefore, preferably the nitroparaffin is present in anamount of from about 2 to about 50% by weight of the modified polyamineresin, and more preferably from about 15 to about 25% by weight of themodified polyamine resin.

Not being bound by theory, it is believed that nitroparaffins rendermodified polyamine resins reducible by water by forming a complex withthe modified polyamine resin, the complex allowing the modifiedpolyamine resin to accept water.

Epoxy resins suitable for use in this invention are those which containmore than one epoxide group and which can be cured by means of theaforementioned modified polyamine resin curing agent. In thisconnection, polyglycidyl ethers of aromatic and aliphatic polyvalenthydroxyl-compounds are commonly used. Some of the more useful types arecomplex polymeric reaction products of polyhydric phenols withpolyfunctional halohydrins and/or glycerol dichlorohydrin.

An important class of epoxy resins useful in the present invention isobtained by reacting trimethanol propane or glycerin withepichlorohydrin. Typical polyhydric phenols used in the preparation ofepoxy resins include resorcinol and various bisphenols resulting fromthe condensation of phenol with aldehydes or ketones such asformaldehyde, acetaldehyde, acetone, methyl ethyl ketone and the like. Acommon epoxy resin is the reaction product of epichlorohydrin and 2,2'-bis(p-hydroxphenyl)-propane, commonly known as the diglycidyl etherof Bisphenol A (DGEBA). Also, suitable epoxy resins can be prepared asthe reaction products of epichlorohydrin andbis(tetra-hydroxphenyl)-sulfone. The glycidyl ethers of polymeric fattyacids obtained by reacting fatty acids having from 8 to 22 carbon atomswith epichlorohydin are also commercially available and are suitableepoxide materials. Another subclass of suitable epoxy resins are Novolacresins produced by condensing phenol and an aldehyde in the presence ofan acid catalyst and subjecting the reaction product to a condensationreaction with epichlorohydrin. Other suitable epoxy resins for use inthe present invention include epoxy resins based on4,4'-isopropylidenedicyclohexanol, those based on hydantoin, anitrogen-containing heterocyclic ring, and polyepoxides obtained byepoxidation of aliphatic and/or cyclo-aliphatic polyolefins.

While certain specified epoxy resins which are most readily availablehave been described, it is understood that other epoxy compounds notspecifically mentioned herein are suitable in the present invention.Also it is not essential to select a single epoxy compound. Mixtures oftwo or more similar and/or different epoxy compounds can be used toattain properties not attainable with a single epoxy compound.

Reactive diluents can also be used in the composition. For example,monoepoxy can be used to reduce the functionality or reactivity of theresin system. Some common monoepoxy diluents are butylglycidylether,diglycidyl ether, allylglycidyl ether, glycidyl acrylate, phenylglycidyl ether, resorcinol glycidyl ether, and butyl phenol cresylether. Also suitable as a monoepoxy diluent is styrene oxide.

Some epoxy resins can be used as reactive dilutents for epoxy resins,without lowering the functionality of the resin system. Some such resinsare vinyl cyclohexene dioxide, diglycidyl ether of 1, 4-butanediol, bis(2,3-epoxycyclopentol) ether, triglycidyl ether of trimethyol propane,and the like which serve to reduce resin viscosity.

Sufficient water is included in the composition to reduce the viscosityof the composition to a level that the composition can easily be appliedas a coating to a surface. By use of nitroparaffin in amounts as low as5 parts nitroparaffin to 100 parts by weight polyamide resin, water inan amount of 500% by weight of the polyamide resin routinely can beadded to coating compositions of the present invention. It is possibleto add as much water as 1500% by weight of the polyamide resin tocoating compositions.

It is possible to use surfactants such as emulsifiers, dispersants, andwetting agents in the composition of the present invention. However,surfactants are not needed for emulsification of the epoxy resin due tothe presence of the nitroparaffin. Preferably surfactants are not usedbecause they tend to adversely affect the water resistance of coatings.As used herein, the term "surfactant" refers to an additive whichreduces surface tension. Dispersants are surfactants that increase thestability of a suspension of solids in a liquid medium. Emulsifiers aresurfactants that modify the surface tension of colloidal droplets anddisperse dissimilar materials ordinarily immiscible to produce a stableemulsion. Nitroparrafins are not considered to be surfactants,dispersants, or emulsifiers herein because it is believed thatnitroparrafins do not affect the surface tension of any component of thecomposition of the present invention.

The modified polyamine and epoxy resins can be used with or without asolvent diluent. Diluents can be used to control viscosity, improvehandling characteristics and/or add bulk for convenient volumes. Forexample, an organic solvent can be used for the modified polyamineresin. Modified polyamine resins are alcohol soluble; thus, a hydroxylicsolvent can be used as a primary solvent. These include ethyl alcohol,isopropyl alcohol, butyl alcohol, 2-butoxy ethanol, monoethyl ether ofdiethylene glycol, ethylene glycol of monobutyl ether (known as butylcellosolve), tetrahydrofuryl alcohol, and the like. A secondary solventcan also be used, including aliphatic, naphthenic and aromatichydrocarbons, ethers, esters, ketones such as ethylene glycol monoethylether, oxylene, dioxane, ethyl acetate, isopropyl acetate, butylacetate, amyl acetate, acetone, methyl ethyl ketone, methyl isobutylketone, hexane, heptane, octane, methyl cyclohexane, and the like.Preferably at least 5% by weight organic solvent for the modifiedpolyamine resin is used for viscosity control.

Suitable solvents for the epoxy resin include mixtures of polar andnon-polar solvents, such as a ketone and a hydrocarbon. Esters,alcohols, and ethers can be substituted for the hydrocarbon. Typicalketones which can be used include methyl ethyl ketone, methyl isobutylketone, diisobutyl ketone, and the like. Other solvents which can beused include xylene, acetone, dibutylsulfate, nonylphenol, and the like.Combinations of solvents can be used.

In water-based systems according to the present invention, water is theprincipal diluent in reducing the viscosity of the coating compositionfor application. Therefore, only small quantities, if any, of theorganic solvents are used. Preferably the amount of organic solvent usedis sufficiently low that the coating composition as applied has avolatile organic content of less than 450 grams per liter, and morepreferably less than 350 grams per liter, to meet air pollutionregulations.

The coating compositions of the present invention can be provided informulations which produce a clear coating, a high gloss coating, apigmented coating, or a coating suitable as a primer. The compositionscan use reaction accelerators and inert, finely divided solids.

Suitable finely divided inert solid materials include fillers, such asasbestos, albality, silica, mica, flint powder, quartz, cryolite,Portland cement, limestone, atomized alumina, barytes, talc, zincpowder, pyrophyllite, various clays, diatomaceous earth, and other likematerials. Pigments, such as titanium dioxide; cadmium red; carbonblack; alumninum powder; and the like also can be used.

Suitable anticorrosive pigments can be added. Typical of these are zincpowder, zinc oxide, red lead, basic lead silica chromate, basic zincchromate, zinc, lead, barium and strontium chromates, calcium plumbate,barium metaborate, and calcium, strontium and zinc molybdates.

Suitable other colorants can be added. Typical of these are: NationalFast Red (National Aniline); Calco Condensation Blue (AmericanCyanamid); Bismark Brown (National Aniline); Blue Lake (13% Ponsal Blue,10% aluminum hydrate and 77% blanc fixe), Krebs BP01790D, Blue LakeKrebs BP-258-D. Lithol Tower, Chrome Yellow, Iron Blue, Milari Blue,Monastral Green, Maroon Toner, Chrome Green, Chrome Orange, Iron OxideReds, Aluminum Powder, and flatting agents like diatomaceous silican andsilica aerogel can be used. The color materials should be selected,however, so as to be non-reactive with the epoxy and modified polyamineresins and other ingredients, as otherwise this might cause poor storagestability.

The finely divided inert solid materials suitable for use herein mayhave an average particle size ranging between about 50 mesh and 400mesh, and preferably between about 100 and 400 mesh (U.S. Std. Series).The exact size of the inert finely divided solid materials depends uponthe particular application of the compositions.

In addition to finely divided solid materials, a wide variety ofresinous modifiers can be added to the epoxy resin systems disclosedherein. Among these are the phenolic resins, such as anilineformaldehyde resins; urea resins, such as urea formaldehyde resins;melamine resins, such as melamine formaldehyde resins; acrylic resins,such as polymethylmethacrylate; polyester resins, such as those producedfrom polybasic acids and polyhydroxyl alcohols and which may containfree carboxyl groups and/or aliphatic hydroxyls capable or reacting withthe epoxy resins; vinyl resins such as vinyl chloride, vinylidenechloride and the like; bituminous resins; and polystyrene. The resinousmodifiers may vary from about 1 to about 100 percent or more by weight,based on the weight of the epoxy resin.

Coating compositions of the present invention can be provided as a kitof two containers. The first container contains the modified polyamineresin and the second container contains epoxy resin curable by themodified polyamine resin. The nitroparaffin can be included in eitherthe first or second container. Sufficient nitroparaffin is provided sothat when the contents of the two containers are combined in aboutstoichiometric proportions to form a coating, water in an amount of atleast 50% by weight of the modified polyamine resin can be added to thecoating composition. Preferably the nitroparaffin is provided with theepoxy resin because interaction between the nitroparaffin and modifiedpolyamine resin can shorten the shelf life of the product.

For the curing of epoxy resins, the curing agent is usually added in astoichiometric quantity, i.e. in an amount that there is one reactive NHgroup in the curing component for each epoxy group in the epoxy resincomponent. Subtle differences in the chemical and physical properties ofeach component prevent precise optimum ratios of the components frombeing specified. It is preferred that ratios of amine N-H to epoxy offrom about 0.7 to about 1.1:1 be used.

Water can be packaged in either the container containing the curingagent or the container containing the epoxy resins. However, no waterneed be packaged with either component. Preferably the water is addedduring catalization to minimize the volume of the packaged product andincrease shelf stability. The contents of the two containers can becombined and then water can be added to the combination. Alternatively,water can be combined with the contents of one of the containers and thecontents of the other container can be added to this combination.Alternatively, water can be combined with the contents of bothcontainers and the two combinations can be combined.

One method of packaging water with the epoxy resin is to emulsify theepoxy resin with suitable emulsifiers (such as Triton X-405 from Rohmand Haas) to form a stable oil-in-water emulsion. Water can be packagedwith the modified polyamine curing agent by including in that packagesome or all of the nitroparaffin. Only when the coating system iscatalized (by mixing the two components) and reduced with water forapplication, does the system take on the true character of a waterreducible coating.

The water reduced coating composition can be applied using conventionalcoating methods including brush-coating, spray coating, and air coating.

The coating compositions of the present invention can be used whereversolvent-based epoxy resin coating compositions are conventionally used.Such uses include application for corrosion protection to structuralsurfaces including buildings, process vessels, ships, airplanes, and thelike. The compositions can also be used as decorative coatings wheredurable coatings are required.

The following examples demonstrate advantages of the present invention.EXAMPLES 1-14

Coating compositions were formed using epoxy resin, modified polyamineresin, and nitroparaffin. Table 1 presents the amount and type of epoxyresin and polyamide resin, and the type of nitroparaffin used for eachexample. Table 2 presents the amount of nitroparaffin used for eachexample. In forming coatings 1-11, the epoxy resin was dissolved in theamount of the xylene presented in Table 1 to make Part A. The polyamideresin was reduced with the amount of butyl cellosolve presented in Table1 and the amount of nitroparaffin presented in Table 2 to make Part B.For coatings 12 and 13, the same procedure was used, except thenitroparaffin was included in Part A. Parts A and B were mixed togetherand the amount of water presented in Table 2 was slowly added whilemixing until a viscosity of 30 seconds Zahn No. 2 cup vixcosity wasattained. After 30 minutes, the mixture was applied by air spray toaluminum panels. After the coating had cured for 1 and 7 days, pencilhardness and resistance to MEK were determined. The coating was alsosprayed on a black sealed leneta card and the 60 degree gloss wasdetermined. The results of these tests are presented in Table 2.

With reference to Table 2, pencil hardness refers to the hardness of thepencil required to make a visible scratch on the coating. The scaleused, from the softest to hardest, is as follows: 6B, 5B, 4B, 3B, 2B, B,HB, F, H, 2H, 3H . . . .

The double MEK rub test involved rubbing a soft cloth soaked in MEK backand forth across the coating. The number in Table 2 represents thenumber of cycles (a back and forth motion) required to visibly softenand remove the coating to the substrate. The gloss values presented inTable 2 were determined with a Gardner Multi-Angle Gloss Meter.

The Epon 828, and 1001 and Eponex 1513 resins used are epoxy resinsavailable from Shell Chemical Company. Araldite EPN-1139 is an epoxyresin available from Ciba Products Co., Ciba-Geigy Corp.

The Versamid polyamide resins used are available from General MillsCorporation. Versamid 100 has an amine value of from about 85 to 95.Versamid 115 has an amine value of from about 230 to 246. Versamid 125has an amine value of from about 330 to 360. Versamid 140 has an aminevalue of from about 370 to 400. Versamid 280-B75 has an amine value offrom about 240 to 260. Versamid 1540 has an amine value of from about370 to 400. For example 12, the polyamide resin component contained 375parts by weight aluminum paste, trade name Silberline 3666. The aluminumpaste was added in after the Versamid 115 was dissolved in the butylcellosolve.

The coating produced in Example 13 was a gloss white coating due to thepresence of titanium dioxide. Dupont R-960 titanium dioxide was includedin the polyamide resin in an amount of 600 parts by weight. Part A wasprepared by mixing Versamid 115, the butyl cellosolve, and xylene untilthe Versamid 115 was dissolved, and then titanium dioxide was mixed intothe composition. This composition was then mixed thoroughly and groundin a pebble mill to 7+ grind.

From the results presented in Table 2, it is evident that by includingnitroparaffin in compositions of the present invention, it is possibleto reduce them with water. Large quantities of water can be added to thecompositions. For example, in Example 3C, 1700 pbw of water were added,based on the amount of polyamide resin. However, as demonstrated byExamples 1A, 2A, 3A, 4A, 5A, 6A, 7A, 8A, 9A, 10A, and 11A, without thenitroparaffin present, the compositions were unable to accept water.What occurred was the polyamide resin formed a separate phase and couldnot be homogeneously dispersed in the water.

The results of Table 2 also demonstrate that the compositions of thepresent invention can produce high gloss, hard, solvent resistantcoatings.

EXAMPLE 15

A coating composition was formed using an epoxy polyamide adduct,diglycidyl ether of bisphenol A (available from Shell Chemical Co. asEpon 834), and 2-nitropropane for use as a corrosion resistant coatingand primer. The coating consisted of:

    ______________________________________                                        First Component   Parts by Weight                                             ______________________________________                                        Epoxy polyamide adduct                                                                          415                                                         Xylene            204                                                         Titanium dioxide   50                                                         Barium Chromate   300                                                         Talc              270                                                         Diatamaceous Silica                                                                              45                                                         ______________________________________                                    

    ______________________________________                                        Second Component                                                                              Parts by Weight                                               ______________________________________                                        Diglycidyl ether of                                                                           357                                                           bisphenol A                                                                   2-nitropropane  70                                                            xylene          45                                                            ______________________________________                                    

The epoxy-polyamide adduct had an average expoxide equivalent value of225. It was prepared by mixing (1) 60 parts by weightpoly-amino-imidazoline having an amine number of 385 (available fromGeneral Mills under tradename Versamid 140), (2) 12 parts diglycidylether of bisphenol A, and 28 parts 2-butoxyethanol. The mixture wasallowed to stand at room temperature for 7 days.

To form a coating, 1 volume of the second component and 2 volumes of thefirst component were mixed together. To this mixture there were addedslowly, while mixing, 31/4 volumes of water. This admix was allowed tostand 30 minutes before using. For spray applications, sufficient waterwas added so that the initial viscosity was 22 to 24 seconds (#2 ZahnCup). The admix contained about 39% solids, had a volatile organiccontent of about 345 grams per liter, and a pot life of 4 to 6 hours.

A coating from 0.6 to 0.9 mils was applied over aluminium panelsconforming to QQ-A-250/4 treated to conform to Mil-C-5541. The coatinghad the following properties:

Drying Times

Tach Free--2 Hours

Print Free--4 Hours

227 Tapetime--5 Hours

Film Hardness--Pencil

HB at 24 Hours

H at 7 Days

MEK resistance--100+ double rubs

Adhesion (Tape Test)--Pass

(Scrape Test)--Pass

Flexibility (G.E.)--Pass 60

Fluid Immersion Resistance

Mil-L-23699--Pass

Mil-H-5606--Pass

Mil-H-83282--Pass

Salt Spray Resistance (ASTM-B-117)

1000 Hours--No Corrosion

From the foregoing discussion and examples, it is apparent that thecompositions of the present invention have many advantages compared toprior art coating compositions. For example, by using nitroparaffin, itis possible to obtain a stable, water-reducible composition thatcontains both modified polyamine resin and epoxy resin. It wassurprising that nitroparaffin, by itself and without the use ofemulsifiers, acts to render modified polyamine resins water reducibleand allows epoxy resins to be emulsified. By eliminating the need foremulsifiers and because the nitroparaffin evaporates from the coatingcomposition as it cures, coatings without water sensitivity can beprepared.

Another advantage of compositions according to the present invention isreduction of the problem of solvent toxicity and fire hazards. Also, thecompositions have a long shelf and pot life. It is easy to control theviscosity of the compositions merely by adding water. Compositionshaving a high gloss, in excess of 90, can be obtained.

The coatings produced and the compositions containing nitroparaffin havea wide variety of uses due to their excellent physical and chemicalproperties. They can be used for decorative and protective purposes onstructures including process vessels and equipment, ships, airplanes,and the like.

Although the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. Therefore, the spirit and scope of the appended claims are notnecessarily limited to the description of the preferred versionscontained herein.

                                      TABLE 1                                     __________________________________________________________________________                        EXAMPLE                                                                       1  2  3  4  5  6  7   8  9  10 11 12 13 14                __________________________________________________________________________    EPOXY RESIN COMPONENT (pbw).sup.a                                             Epon 828            247                                                                              247                                                                              247                                                                              247                                                                              -  -  184 -  304                                                                              323                                                                              285                                                                              320                                                                              320                                                                              -                 Epon 1001           -  -  -  -  380                                                                              -  -   482                                                                              -  -  -  -  -  -                 Araldite EPN - 1139 -  -  -  -  -  228                                                                              -   -  -  -  -  -  -  -                 Eponex 1513         -  -  -  -  -  -  -   -  -  -  -  -  -  352.5             Xylene              106                                                                              106                                                                              106                                                                              106                                                                              127                                                                              106                                                                              119 266                                                                              110                                                                              110                                                                              125                                                                               53                                                                               53                                                                              132               MODIFIED POLYAMINE                                                             RESIN COMPONENT (pbw)                                                        Versamid 1540       -  -  -  -  -  -  -   -  -  -  -  -  -  217.5             Versamid 115        305                                                                              305                                                                              305                                                                              305                                                                              178                                                                              305                                                                              -   -  -  -  -  400                                                                              400                                                                              -                 Versamid 125        -  -  -  -  -  -  -   -  260                                                                              -  -  -  -  -                 Versamid 140        -  -  -  -  -  -  -   -  -  246                                                                              -  -  -  -                 Versamid 280-B75    -  -  -  -  -  -  -   -  -  -  340                                                                              -  -  -                 Versamid 100        -  -  -  -  -  -  600 600                                                                              -  -  -  -  -  -                 Butyl Cellosolve    110                                                                              110                                                                              110                                                                              110                                                                              127                                                                              110                                                                              195 195                                                                              114                                                                              113                                                                               35                                                                              135                                                                              133                                                                              75                Xylene              -  -  -  -  -  -  -   -  -  -  -  -  108                                                                              -                 NITROPARAFFIN                                                                 2-nitropropane      +  -  -  -  +  +  +   +  +  +  +  +  +  +                 1-nitropropane      -  +  -  -  -  -  -   -  -  -  -  -  -  -                 Nitroethane         -  -  +  -  -  -  -   -  -  -  -  -  -  -                 Nitromethane        -  -  -  +  -  -  -   -  -  -  -  -  -  -                 __________________________________________________________________________     .sup.a pbw = parts by weight                                             

                                      TABLE 2                                     __________________________________________________________________________                          WATER                                                                         ADDED                                                                              60°                                                                         PENCIL HARDNESS                                                                            MEK RUB                          EXAMPLE #                                                                             NITROPARAFFIN.sup.b (phr)                                                                   (pbw)                                                                              GLOSS                                                                              OVERNIGHT                                                                             7 DAY                                                                              OVERNIGHT                                                                             7 DAY                    __________________________________________________________________________    1A      0             NA.sup.c                                                                           --   --      --   --      --                       1B      5             1600 47   B       F    5       90                       1C      10            2800 82   B       F    15       100+                    1D      20            2400 75   B       F    10       100+                    1E      40            2800 60   B       F    8       35                       2A      0             NA   --   --      --   --      --                       2B      5             2600 65   HB      F    3       50                       2C      10            3000 77   HB      F    4       50                       2D      20            3000 80   HB      F    6       65                       2E      40            2000 89   HB      F    8       85                       3A      1             NA   --   --      --   --      --                       3B      5             2600 61   HB      F    6       65                       3C      10            3400 77   HB      F    5       60                       3D      20            2000 75   HB      F    8       70                       3E      40            1400 75   HB      F    14      55                       4A      0             NA   --   --      --   --      --                       4B      5             2000 65   B       F    <5      30                       4C      10            2800 75   B       F    <5      45                       4D      20            3400 79   HB      F    6       60                       4E      40            3000 78   HB      F    5       55                       5A      0             NA   --   --      --   --      --                       5B      10            1200 .sup.d                                                                             --      --   --      --                       5C      20            1200 87   B       F    <5      24                       5D      40            1200 89   B       F    <5      25                       6A      0             NA   --   --      --   --      --                       6B      5             1600 63   2B      F    6       20                       6C      10            2800 57   2B      F    6       20                       6D      20            2800 68   2B      F    5       20                       7A      0             NA   --   --      --   --      --                       7B      1             1200 .sup.d                                                                             --      --   --      --                       7C      2             1200 95   2B      F    <5      60                       7D      4             2400 90   2B      F    <5      25                       7E      8             3600 83   B       F    <5      25                       8A      0             NA   --   --      --   --      --                       8B      1               800                                                                              93   2B      F    5       30                       8C      2              800 95   2B      F    5       25                       8D      4             1600 95   B       F    5       25                       8E      8             2800 95   HB      F    5       27                       9A      0             NA   --   --      --   --      --                       9B      5             2400 gell.sup.e                                                                         B       F    5       45                       9C      10            2400 .sup. 25.sup.e                                                                     B       F    6       50                       9D      20            2000 .sup. 52.sup.e                                                                     B       F    5       40                       10A     0             NA   --   --      --   --      --                       10B     5             1800 gell.sup.e                                                                         B       HB   <5      30                       10C     10            1200 gell.sup.e                                                                         B       HB   <5      30                       10D     20            1000 .sup. 76.sup.e                                                                     B       HB   <5      45                       11A     0             NA   --   --      --   --      --                       11B     5             1200 90   B       F    12       100+                    11C     10            1200 89   B       F    15       100+                    11D     20            1200 85   B       F    14       100+                    12      20            2400 --   HB      F    15      60                       13      20            2400 96   B       F    15      60                       14A     0             NA   --   --      --   --      --                       14B     5             1200 96   B       HB   10      50                       14C     10             900 98   B       HB   12      100                      14D     20             900 96   B       HB   16      110                      __________________________________________________________________________     .sup.b phr = parts nitroparaffin per onehundred parts polyamide resin.        .sup.c NA = does not accept water.                                            .sup.d Poor film properties.                                                  .sup.e 3 hours.                                                          

What is claimed is:
 1. A homogeneous water-reducible coating compositioncomprising epoxy resin and sufficient modified polyamine resin to curethe epoxy resin, the modified polyamine resin being a polyamide-epoxyadduct formed by reacting a poly-amino-imidazoline and diglycidyl etherof bisphenol A, the modified polyamine resin being homogeneously reducedin an aqueous system comprising nitroparaffin in an amount of at least2% by weight of the modified polyamine resin and water in an amount ofat least 50% by weight of the modified polyamine resin, the compositioncontaining substantially no emulsifier, the nitroparaffin having theformula C_(n) X_(2n+2) where n is an integer from 1 to 4 and each X isindependently selected from the group consisting of chlorine, hydrogen,and NO₂, where at least one but no more than two X's are NO₂, themodified polyamine resin being inherently insoluble and non-dispersiblein water.
 2. The composition of claim 1 in which the nitroparaffin isselected from the group consisting of nitromethane, nitroethane,1-nitropropane, 2-nitropropane, 1-nitrobutane, 2-nitrobutane, andcombinations thereof.
 3. The composition of claim 2 in which thenitroparaffin is 2-nitropropane.
 4. The composition of claim 1 in whichthe modified polyamine resin is inherently incapable of beinghomogeneously reduced by water.
 5. The composition of claim 1 comprisingthe nitroparaffin in an amount of up to 50% by weight of the modifiedpolyamine resin.
 6. The composition of claim 1 comprising thenitroparaffin in an amount of from about 15 to about 25% by weight ofthe modified polyamine resin.
 7. The composition of claim 1 in which themodified polyamine resin has an amine value of less than about
 400. 8.The composition of claim 1 having a volatile or anic content of no morethan 450 grams per liter.
 9. The composition of claim 8 including anorganic solvent for the epoxy resin.
 10. The composition of claim 8including an organic solvent for the modified polyamine resin.
 11. Ahomogeneous, water-reduced coating composition comprising:(a) epoxyresin; (b) sufficient moified polyamine resin to cure the epoxy resin,wherein the modified polyamine resin (i) is a polyamide-epoxy adductformed by reacting a poly-amine-imidazoline and diglycidyl ether ofbisphenol A, (ii) has an amine value of less than about 400, and (iii)is inherently incapable of being reduced, dissolved, or dispersed bywater; and (c) an aqueous system in which the modified polyamine resinis homogeneously reduced, the aqueous system comprising an organicsolvent for the modified polyamine resin, nitroethane in an amount offrom about 15% to about 25% by weight of the modified polyamine resin,and water in an amount of at least 50% by weight of the modifiedpolyamine resin, the composition containing substantially no emulsifierand having a volatile organic content of no more than 450 grams perliter.
 12. A composition for forming a coating, the compositioncomprising (a) epoxy resin, (b) nitroparaffin, the nitroparaffin havingthe formula C_(n) X_(2n+2) where n is an integer from 1 to 4 and each Xis independently selected from the group consisting of chlorine,hydrogen, and NO₂, where at least one but no more than two X's are NO₂,and (c) sufficient modified polyamine resin to cure the epoxy resin, thenitroparaffin being present in the composition in an amount sufficientthat the modified polyamine resin is homogeneously reduced by an aqueoussystem comprising water in an amount of at least 50% by weight of themodified polyamine resin, the composition containing substantially noemulsifier and having a volatile organic content of less than 450 gramsper liter, the modified polyamine resin being inherently insoluble andnon-dispersible in water.
 13. A composition for forming a coating, thecomposition containing substantially no emulsifier and comprising (a)epoxy resin, (b) nitroparaffin selected from the group consisting ofnitromethane, nitroethane, 1-nitropropane, 1-nitrobutane, 2-nitrobutane,and combinations thereof, and (c) sufficient modified polyamine resin tocure the epoxy resin, the nitroparaffin being present in the compositionin an amount sufficient that the modified polyamine resin ishomogeneously dispersed in an aqueous system comprising water in anamount of at least 50% by weight of the modified polyamine resin, thecomposition having a volatile organic content of less than 450 grams perliter, the modified polyamine resin being inherently insoluble andnon-dispersible in water.
 14. The composition of claim 12 in which thenitroparaffin is selected from the group consisting of nitromethane,nitroethane, 1-nitropropane, 2-nitropropane, 1-nitrobutane,2-nitrobutane, and combinations thereof.
 15. The composition of claim 13in which the nitroparaffin is 2-nitropropane.
 16. The composition ofclaim 12 or 13 in which the nitroparaffin is nitroethane.
 17. Thecomposition of claim 12 including an organic solvent for the epoxyresin.
 18. The composition of claim 12 including an organic solvent forthe epoxy resin.
 19. The composition of claims 12, 13, 17 or 18 having avolatile organic content of no more than 350 grams per liter.
 20. Ahomogeneous composition comprising modified polyamine resin curing agentfor epoxy resins, the modified polyamine resin being a polyamide-epoxyadduct formed by reacting a poly-amino-imidazoline and diglycidyl etherof bisphenol A, the modified polyamine resin being homogeneously reducedin an aqueous system comprising water in an amount of at least 50% byweight of the modified polyamine resin and nitroparaffin in an amount ofat least 2% by weight of the modified polyamine resin, the compositioncontaining substantially no emulsifier, the nitroparaffin having theformula C_(n) X_(2n+2) where n is an integer from 1 to 4 and each X isindependently selected from the group consisting of chlorine, hydrogen,and NO₂, where at least one but no more than two X's are NO₂, themodified polyamine resin being inherently insoluble and non-dispersiblein water.
 21. The composition of claim 20 or 30 in which thenitroparaffin is selected from the group consisting of nitromethane,nitroethane, 1-nitropropane, 2-nitropropane, 1-nitrobutane,2-nitrobutane, and combinations thereof.
 22. The composition of claims1, 20 or 21 in which the nitroparaffin is nitroethane.
 23. Thecomposition of claim 20 or 21 in which the modified polyamine resin isinherently incapable of being homogeneously reduced by water.
 24. Thecomposition of claim 20 or 21 comprising the nitroparaffin in an amountof up to 50% by weight of a modified polyamine resin.
 25. Thecomposition of claim 20 or 21 in which the modified polyamine resin hasan amine value of less than about
 400. 26. The composition of claim 20or 21 including an organic solvent for the polyamine resin.
 27. Thecomposition of claim 20 or 21 having a volatile organic content of nomore than 450 grams per liter.
 28. The composition of claim 20 or 21including epoxy resin in an amount about stoichiometric to the amount ofpolyamide resin in the composition.
 29. A homogeneous compositioncomprising modified polyamine resin having an amine value of less thanabout 400 homogeneously reduced in an aqueous system comprising (i)water in an amount of at least 50% by weight of the modified polyamineresin, (ii) nitroethane in an amount of from about 15 to about 25% byweight of the modified polyamine resin, and (iii) an organic solvent forthe modified polyamine resin, the composition containing substantiallyno emulsifier wherein the modified polyamine resin is inherentlyincapable of being homogeneously reduced, dissolved, or dispersed bywater, and the composition has a volatile organic content of no morethan about 450 grams per liter, the modified polyamine resin being apolyamide-epoxy adduct formed by reacting a poly-amino-imidazoline anddiglycydl ether of bisphenol A.
 30. A homogeneous, water-reduciblecomposition comprising modified polyamine resin curing agent for epoxyresins and nitroparaffin in an amount sufficient that the modifiedpolyamine resin can be homogeneously reduced by water in an amount of atleast 50% by weight of the modified polyamine resin, the modifiedpolyamine resin being a polyamide epoxy adduct formed by reacting apoly-amino-imidazoline and diglycidyl ether of bisphenol A, thecomposition containing substantially no emulsifier and having a volatileorganic content of less than 450 grams per liter, the modified polyamineresin being inherently insoluble and non-dispersible in water, thenitroparaffin having the formula C_(n) X_(2n+2) where an is an integerfrom 1 to 4 and each X is independently selected from the groupconsisting of chlorine, hydrogen, and NO₂, where at least one but nomore than two X's are NO₂.
 31. The composition of claim 12 or 13 inwhich the modified polyamine resin is inherently incapable of beinghomogeneously reduced by water.